Method and arrangement for handling and processing substrates

ABSTRACT

The invention relates to a substrate handling and exposure arrangement comprising a plurality of lithography apparatus, a clamp preparation unit for clamping a wafer on a wafer support structure, a wafer track, wherein the clamp preparation unit is configured for accepting a wafer from the wafer track, and an additional wafer track for transferring the clamp towards the plurality of lithography apparatus.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/708,543 filed on Feb. 19, 2010, now U.S. Pat. No. ______, whichclaims priority to U.S. provisional application No. 61/154,411 filed onFeb. 22, 2009, and British application no. GB 0905786.0 filed on Apr. 3,2009. All applications are hereby incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of clamping a substrate on asurface of a substrate support structure, a clamp preparation unitconfigured to clamp a substrate to a substrate support structure, and alithography system comprising such a clamp preparation unit.

2. Description of the Related Art

Clamping of a substrate, for example a wafer, onto a surface of asubstrate support structure, for example a wafer table, is well known inthe semiconductor industry, and in particular in lithography systems. Insuch lithography systems, the clamped substrate is to be patterned bymeans of subjection to incident photons or charged particles like ionsand/or electrons. The clamping ensures the realization of high precisionpatterning of a target portion of the substrate surface. Preferably,position control by using clamping is not only used during exposure, butalso during handling of the substrate, for example during insertion intoand/or removal from the exposure chamber within the lithographic system.

Clamping may be achieved by sucking away air between the substrate andthe substrate support structure, i.e. by creating a vacuum in between.However, if aforementioned position control is required in a vacuumenvironment, such a clamping mechanism will not be effective. Varioussolutions exist for clamping a substrate in a vacuum environment, forexample by means of electromechanical clamping. It will be understoodthat such a solution is not very suitable for use in combination withone or more beams of charged particles like electrons and/or ions.

International application WO2009/011574 filed by the Applicant,describes a lithography system with a substrate support structure forclamping a substrate by means of a layer of stationary liquid, hereafterreferred to as capillary layer. The thickness of the capillary layer issuch that between the substrate surface and the surface of the substratesupport structure a pressure drop arises. As explained in WO2009/011574,adhesion of the liquid to the surfaces of the substrate on the one handand the substrate support structure on the other hand causes acircumferentially extending liquid surface, concavely extending betweenthe two surfaces. The so-formed concave liquid surface tends to maintainits shape, even if forces are applied to remove the substrate from thesubstrate support structure surface.

Under some special circumstances, the substrate clamping mechanismdescribed in WO2009/011574 does not perform in an optimal manner, e.g.due to the presence of voids in the capillary layer. Furthermore, due toevaporation processes, the capillary layer will be present for a limitedperiod of time. As a result, the clamping mechanism may only be usefulfor a selection of devices to be patterned.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a substrate supportstructure for clamping a substrate on a surface thereof by means of acapillary layer as well as a method of clamping a substrate on a surfaceof a substrate support structure with improved performance. This objecthas been achieved by providing a method of clamping a substrate on asurface of a substrate support structure, the method comprising applyinga liquid on a surface of the substrate support structure, the surfacebeing provided with a plurality of contact elements, so that the liquidforms a layer covering the contact elements; providing the substrate andplacing the substrate onto the liquid layer; and removing a portion ofthe liquid from under the substrate so that the substrate rests on theplurality of contact elements and is clamped by means of a capillaryclamping force exerted by a capillary layer of the liquid between thesubstrate and the surface of the substrate support structure.

According to another aspect of the invention, a clamp preparation unitfor clamping a substrate comprises: a substrate support structure havinga surface provided with a plurality of contact elements; a liquiddispensing unit for applying a liquid on to the surface of the substratesupport structure, so that the contact elements are covered by a liquidlayer; a substrate transfer unit for placing the substrate on to theliquid layer; and a liquid removal system for removing a portion of theliquid from under the substrate so that the substrate rests on theplurality of contact elements and is clamped by means of a capillaryclamping force exerted by a capillary layer of the liquid between thesubstrate and the surface of the substrate support structure.

According to yet another aspect of the invention, a method of unclampinga substrate from a substrate support structure is provided, where thesubstrate is clamped by means of a capillary clamping force exerted by acapillary layer of liquid between the substrate and a surface of thesubstrate support structure. The method comprises: providing additionalliquid to the capillary layer at an outer circumferential surface of thecapillary layer; and lifting the substrate from the liquid.

According to yet another aspect of the invention, an unclamping unitcomprises: a substrate support structure having a substrate clamped on asurface of the substrate support structure by means of a capillarylayer; a liquid removal system for providing additional liquid to thecapillary layer under the substrate at an outer circumferential surfaceof the capillary layer; and a substrate transfer unit for removing thesubstrate from the liquid layer.

According to yet another aspect of the invention, a lithography systemincluding a lithographic apparatus comprises: a radiation system toprovide a patterned beam of radiation; an optical system to project thepatterned beam of radiation onto a target portion of a substrate; and aclamp preparation unit for clamping the substrate to a surface of asubstrate support structure. The lithography system may also include anunclamping unit.

It will be evident that the presently invented principle may be set intopractice in various manners.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the invention will be further explained withreference to embodiments shown in the drawings wherein:

FIG. 1 is a sectional view schematically illustrating a capillary layerbetween two structures;

FIG. 2 is a sectional view schematically illustrating processes with anegative impact on the clamp stability of the capillary layer of FIG. 1;

FIG. 3A is a sectional view of a substrate support structure accordingto a first embodiment of the invention;

FIG. 3B is a top view of the substrate support structure of FIG. 3A;

FIG. 4 schematically illustrates the concept of substrate peeling;

FIG. 5 is a sectional view of a substrate support structure supporting asubstrate according to a second embodiment of the invention;

FIGS. 6A-6C are top views of the substrate support structure of FIG. 5further schematically illustrating the concept of reclamping;

FIGS. 7A-7J schematically show execution of a method of clamping asubstrate on a surface of a substrate support according to an embodimentof the invention;

FIG. 8A schematically shows a top view of a substrate support structureaccording to a third embodiment of the invention;

FIG. 8B schematically shows a sectional view of a clamp formed by acombination of the substrate support structure of FIG. 8A and asubstrate;

FIG. 9 schematically shows a substrate handling and exposure arrangementwhich may be used in conjunction with embodiments of the substratesupport structure;

FIG. 10 schematically shows a different substrate handling and exposurearrangement that may be used in conjunction with embodiments of thesubstrate support structure.

FIGS. 11A-11D schematically show operation of an exemplary clamppreparation unit to be used in the substrate handling and exposurearrangement of FIG. 9 or FIG. 10.

In the figures, corresponding structural features, i.e. at leastfunctionally, are referred to by identical reference numbers.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The following is a description of various embodiments of the invention,given by way of example only and with reference to the drawings.

FIG. 1 is a sectional view schematically illustrating a capillary liquidlayer 1 of a capillary liquid, e.g. water, between a first substrate 2,e.g. a wafer, and a second substrate 3, e.g. a substrate supportstructure like a wafer table. The first and second substrates 2, 3 havea substantially flat surface 5, 6 respectively. The nominal distancebetween the opposing surfaces 5, 6 of the first and second substrates 2,3 is given by height h. The capillary liquid layer 1 has an outer liquidsurface 8, which is generally concavely shaped due to adhesiveconnection of the liquid to the first substrate 2 and the secondsubstrate 3.

The concave liquid surface 8 tends to maintain its shape if the firstsubstrate 2 and the second substrate 3 are subject to forces in adirection substantially perpendicular to the opposing surfaces 5, 6. Theconcaveness of the outer liquid surface 8 depends on the contact anglebetween the capillary layer 1 and the surface 5 of the first substrate2, and on the contact angle between the capillary layer 1 and thesurface 6 of the second substrate 3. The respective contact anglesdepend on the liquid used in the capillary layer 1 as well as on thematerial properties of the two substrates 2, 3. More details withrespect to a capillary layer holding together two structures withsubstantially flat opposing surface is provided in international patentapplication WO2009/011574, which is incorporated herein in its entirety.

FIG. 2 is a sectional view schematically illustrating processes with anegative impact on the stability of the clamping action performed bymeans of the capillary liquid layer 1 of FIG. 1. Hereafter, theexpression “clamp” will be used for the arrangement where the substrate2 is clamped to the substrate support structure 3 by means of thecapillary layer 1.

If pre-existing bubbles are present in the liquid, introduction of theclamp into a vacuum environment will lead to expansion of such bubbleswithin the capillary layer. The size of initially small bubbles can growby several orders of magnitude if ambient pressure decreases, e.g. from1 bar to 10⁻⁶ mbar. As can be readily seen in FIG. 2, a bubble of thesize of bubble 11 may seriously influence the clamping strength, atleast locally, and may have a negative influence on the stability of theclamp.

Another mechanism that may lead to clamp instability is spontaneous voidformation, for example caused by cavitation of or dissolved gasprecipitation in the capillary liquid layer. An example of such a voidhas been denoted by reference numeral 13 in FIG. 2. Voids formed bycavitation may grow in a similar way as discussed before with respect topre-existing bubbles if the clamp is brought into a vacuum environment.The resulting voids may have a negative influence on the clampstability.

Besides decrease of the clamp stability due to the presence of bubblesand/or voids, the clamp stability will also be negatively affected byevaporation of liquid at the capillary layer interface, i.e. evaporationat the concave liquid surface. FIG. 2 schematically shows the effect ofsuch evaporation. Due to evaporation, the position of the outer liquidsurface 8 has shifted towards a new position to form outer liquidsurface 8′. As a result of that shift, the surface area covered by thecapillary layer, and thus the stability of the clamp, has decreased.

FIGS. 3A and 3B are a sectional view and a top view of a substratesupport structure 23 supporting a substrate according to a firstembodiment of the invention respectively. The support structure isequipped to clamp a substrate 22 by means of a capillary layer 21. Thesurface 26 of the substrate support structure 23 is provided with aplurality of contact elements 27 in the form of burls. The substratesupport structure 23 further comprises a sealing structure 29 and aliquid removal system.

In addition to or instead of using burls as contact elements 27, aplurality of spacers, e.g. glass grains, SiO₂ grains or the like may bedispersed uniformly over the surface 26 of the substrate supportstructure 23. The presence of contact elements like burls may reduce theinfluence of contamination by particles on the backside of the substrate22. Furthermore, the contact elements serve the purpose of keeping thesubstrate 22 substantially flat by withstanding the clamping force ofthe capillary layer to prevent the occurrence of substrate bow.

The maximum pitch of contact elements 27 is determined by therequirements set for the maximum deflection of the substrate betweenadjacent contact elements caused by the clamping force of the capillarylayer. The contact surface per contact element is such that it issufficient to withstand deformation and/or destruction under the appliedclamping pressure. Preferably, edges of a contact element are rounded toreduce the possibility of particle contamination, e.g. during cleaningoperations. A typical value for the diameter of a burl 27 with acircular contact area would be in the range of 10-500 microns. A typicalvalue for the pitch of a plurality of burls 27 would be in the range of1-5 mm.

The nominal height of the contact elements determines the distancebetween the substrate 22 and the surface 26 of the substrate supportstructure 23, and thus the clamping pressure. Other parameters that maybe varied to obtain a desired clamping pressure include materialproperties of the substrate 22, material properties of the surface 26 ofthe substrate support structure 23, surface area of the surface 26,contact element shape, contact element pitch, and the type of liquidused to form a capillary layer 21.

The sealing structure 29 circumscribes the surface 26 of the substratesupport structure 23 facing the substrate 22 to be clamped. The sealingstructure 29 may limit leakage of liquid evaporating from the capillarylayer 21, when present. Preferably, the top side of the sealingstructure 29 has a level corresponding in height with the nominal heightof the plurality of burls 27. Such an arrangement increases theefficiency of vapor leakage prevention, which is in particular an issuein a vacuum environment.

The sealing structure 29 may comprise one or more elastically deformableelements like O-rings, e.g. made of viton or rubber. Such O-rings may beinserted in a part of the substrate support structure 23 with reducedheight such that the top side of the O-ring is set to the levelmentioned above. The O-ring may be provided with an incision at a radialside, e.g. the radial side facing the center of the substrate supportstructure 23, such that the O-ring can be compressed between substratesupport structure 23 and substrate 22 without undue force requirement,but sufficient to prevent leakage of vapor.

Alternatively, as in FIG. 3A, the sealing structure 29 may comprise avapor limiting ring, supported by an outer rim of the substrate supportstructure 23. The vapor limiting ring closes off the circumferentialopening facing the capillary liquid surface, only leaving a very smallvertical distance between the ring and the substrate 22 supported by theplurality of burls 27 on the surface 26 of the substrate supportstructure 23.

The liquid removal system is configured to remove liquid underneath thesubstrate to enable formation of a capillary layer 21. Further detailsregarding the formation of a capillary layer 21 by using a liquidremoval system will be discussed with reference to FIG. 7.

The liquid removal system is configured to remove excess water from thesurface 26 of the substrate support structure 23. In FIG. 3A, the liquidremoval system comprises a gas distribution system, an embodiment ofwhich is partly shown in FIG. 3B. The gas distribution system maycomprise a moat 31 in circumference of the surface 26, one or more gasinlets 33 for allowing gas into the moat 31 and one or more gas outlets35 for removing gas from the moat 31 respectively. If a sealingstructure 29 is present, a gas flow may be established between thesurface 26 provided with a liquid layer and the sealing structure 29,thus forming a channel flow as shown in FIG. 3B by the dashed arrows.

The one or more gas inlets 33 and the one or more gas outlets 35 may beprovided along the moat 31 in a symmetrical fashion. In the embodimentof FIG. 3B, there are two gas inlets 33 and two gas outlets 35. The gasinlets 33 and gas outlets 35 are positioned in such a way that a firstvirtual line 37 formed by connecting the two gas inlets 33, and a secondvirtual line 39 formed by connecting the two gas outlets 35 aresubstantially perpendicular with respect to each other.

The substrate support structure 23 shown in FIG. 3A further comprises aliquid reservoir 41. The liquid reservoir 41 is configured toaccommodate a certain volume of liquid, for example water, and furtherto store vapor of that liquid. Furthermore, the liquid reservoir isarranged to provide vapor to the capillary layer 21 when present, forexample via one or more channels 43. The reservoir may be referred to asliquid reservoir 41. Preferably, the liquid in the liquid reservoir 41,reservoir liquid, is the same as the liquid within the capillary layer21, i.e. capillary liquid. A suitable liquid for both reservoir liquidand capillary liquid would be water.

The presence of a liquid reservoir provides a way to further decreaseevaporation of liquid from the capillary layer 21 when present. The freesurface area of the liquid in the reservoir is preferably larger thanthe free surface area of the concave outer surface 28 of the capillarylayer 21. The larger free surface area of the liquid stored in thereservoir ensures that a sufficient amount of vapor is available tomoisturize the environment of surface 28, resulting in less vaporizationwithin the capillary layer 21.

The vapor may be transported from the liquid reservoir 41 towards theouter liquid surface 28 of the capillary layer 21 by means of the one ormore gas inlets 33 and/or the one or more gas outlets 35. In such acase, the gas for use in the gas distribution system may be provided tothe substrate support structure via a valve 45 that is also used toprovide liquid to the liquid reservoir 41.

Alternatively, gas may be provided via one or more separate gasconnection units. If such gas connection units are configured to providethe gas flow via the one or more channels 43 used to provide vapor tothe capillary layer, the one or more channels 43 may be provided with aflow control unit 44. Such a flow control unit 44 is configured toseparate gas flow via the gas connection unit from vapor originatingfrom the reservoir 41.

In yet another alternative embodiment, the gas distribution system isentirely separate from the one or more elements to provide the vaporfrom the vapor reservoir 41 to the clamp.

As mentioned earlier with reference to FIG. 2, the layer of capillaryliquid evaporates in a vacuum environment. Experiments have shown thatthe remaining volume of the capillary liquid layer tends to accumulateat one side of the clamp. Due to this asymmetric distribution of thecapillary layer, one side of the substrate “peels off” the table.Hereafter, the effect will be referred to as substrate peeling.

FIG. 4 schematically illustrates the concept of substrate peeling.Without wishing to be bound by theory, it is believed that due tounavoidable random instabilities the edge of the substrate 22 starts tolift away from the substrate support structure 23 at a location wherethe substrate 22 happens to be less strongly clamped. The movement oflifting is schematically represented in FIG. 4 by the arrow 47. Due tothe peeling, vapor may more easily leak away from the capillary layer21. Additionally, the outer liquid surface 28 of the capillary layer 21increases, which leads to an increase in evaporation rate. Furthermore,the local peeling causes the capillary layer 21 to shift away from thearea in which the peeling occurs. This leads to further unclamping.Thus, local peeling may limit the lifetime of the clamp significantly.

FIG. 5 is a sectional view of a substrate support structure 23supporting a substrate 22 according to a second embodiment of theinvention. The embodiment of the substrate support structure 23 of FIG.5 further comprises a circumferential rim 51. The circumferential rim 51provides a smaller distance between the substrate support structure 23and the substrate 22. While the nominal distance between the substratesupport structure 23 and the substrate 22, in FIGS. 1 and 2 referred toas height h, typically is about 3-10 microns, the distance between thecircumferential rim 51 and the substrate 22 typically would lie in therange of 500 nm to 1.5 microns. Preferably, the circumferential rim 51has a height being less than 1 micron smaller than the nominal height ofcontact elements provided on the surface 26 of the substrate supportstructure 23.

Without wishing to being bound by theory, the circumferential rim 51 isbelieved to limit substrate peeling in a way described with reference toFIGS. 6A-6C showing top views of the substrate support provided with acapillary layer. Although the presence of a circumferential rim 51 hasbeen discussed with reference to FIG. 5, the use of such circumferentialrim 51 is not limited to this embodiment. For example, a circumferentialrim 51 may also be applied to the embodiment schematically depicted inFIG. 3A, and embodiments discussed in international patent applicationWO2009/011574.

First, as liquid evaporates from the outer capillary surface 28, it willrecede into the small gap between the circumferential rim 51 and thesubstrate 22. Due to non-uniform evaporation, the outer capillarysurface 28 may locally recede further inwards as schematically shown inFIG. 6A. The capillary pressure jump over the smaller gap between thecircumferential rim 51 and the substrate 22 is much larger than thepressure jump would be in the main clamping area, e.g. about 1 barversus about 200 mbar respectively. When the outer capillary surface 28reaches the inner side surface of the circumferential rim 51 due toevaporation, the surface encounters the larger distance betweensubstrate 22 and substrate support structure 23. The lower capillarypressure jump in this region causes a small amount of liquid to flowinto the gap between the circumferential rim 51 and the substrate 22 asis schematically shown in FIG. 6B. The flow will continue until the gapbetween the circumferential rim 51 and the substrate 22 is completelyfilled as shown in FIG. 6C. A void will be left in the main clampingregion. The void is entirely surrounded by a liquid layer. Effectively,the lost capillary clamping area due to evaporation has been movedinwardly. The outer capillary surface remains at the same position. As aresult, the substrate edge will not peel off.

Embodiments of the substrate support structure 23 like the ones shown inFIGS. 3A and 5, may be designed in such a way that cavitation effectsare minimized or non-existing. Without wishing to be bound by theory, itis understood that there is a critical radius for cavities. If theradius of a cavity becomes larger than this critical radius, the cavitymay grow extensively. By using a substrate support structure thatenables the formation of a capillary layer with a smallest dimension,i.e. a thickness h, that is very small, and preferably smaller than, thecritical radius, cavitation will be largely limited or not occur.Experiments have shown that a capillary layer of water with a thicknessh in the order of 3-10 microns does not experience cavitation.

As a specific measure, one or both of the contacting surfaces of thesubstrate 22 and the substrate support structure 23 may be surfacetreated, or coated with a material for influencing a contacting anglebetween the liquid forming the capillary layer 21 and the relevantcontacting surface.

FIGS. 7A-7J schematically show execution of an embodiment of a method ofclamping a substrate on a surface of a substrate support structureaccording to an embodiment of the invention. The method may be executedin a clamp preparation unit, which allows automation of a method ofclamping a substrate on a substrate support structure.

The clamp preparation unit comprises a vacuum system that is able toprovide a controlled pressure environment. Furthermore, the clamppreparation unit comprises a liquid dispensing unit for applying liquid,one or more gas connection units for providing and removing gas, and oneor more liquid connection units for providing and removing liquid.

As shown in FIG. 7A, first, a substrate support structure 23 is placedin a vacuum chamber, for example a housing within the vacuum system of aclamp preparation unit. After placement of a substrate support structure23 in a vacuum chamber, a liquid is applied on a surface 26 thereof,schematically shown in FIG. 7B. Application of liquid on surface 26 ofthe substrate support structure 23 may be performed by means of a liquiddispensing unit 61.

In FIGS. 7A-7J, the surface 26 of the substrate support structure 23 isprovided with contact elements, e.g. burls 27. In one embodiment,applying the liquid continues at least until the contact elements arecovered by a liquid layer 64. A typical thickness of the liquid layer 64after the applying of liquid is in the range of 2-5 mm. Applying theliquid is preferably performed at a pressure level substantially equalto the vapor pressure of the liquid in the liquid layer 64. Applying theliquid at such pressure reduces the chance of dissolving of gases and/orentrainment of bubbles in the liquid.

Optionally, after applying the liquid, a pausing action is performed.This action is schematically shown in FIG. 7C. The pausing allowsdiffusion of dissolved gases and/or entrained bubbles 62 out of theliquid layer 64. The removal of dissolved gases and/or entrained bubbles62 reduces the chance of formation of voids as discussed with referenceto FIG. 2.

Then, a substrate 22 is placed on top of the liquid layer 64.Preferably, as schematically shown in FIG. 7D, the substrate is placedsuch that an edge at a first end portion 22 a of the substrate 22contacts the liquid layer 64 first at an initial angle, hereafterreferred to as the tilt angle. After the first contact, thenon-contacting end portion 22 b of the substrate 22 is lowered until thesubstrate 22 fully rests on the liquid layer 64 as shown in FIG. 7E.

In FIG. 7D, the substrate 22 is placed at an initial angle α. The liquidcontacts the bottom surface of the substrate 22 and adheres to it due tocapillary effects. In one embodiment, after first contact of one endportion 22 a of the substrate 22, the other end portion 22 b of thesubstrate 22 is lowered such that the water-substrate contact line movesalong the bottom surface of the substrate 22 in the direction of theother end portion 22 b, in FIG. 7D a movement to the right schematicallyillustrated by the arrow. Placement of the substrate 22 at a tilt anglereduces the chance of capturing air or gas between the substrate 22 andthe substrate support structure 23, which improves the stability of theclamp to be established. The tilt angle alpha (α) is an acute angle,preferably smaller than 10 degrees, and preferably greater than 5degrees. Experiments have shown that such a tilt angle providessatisfactory results.

FIG. 7E shows the substrate 22 after placement onto the liquid layer 64.The substrate 22 floats on the liquid layer 64.

After placement of the substrate on top of the liquid layer, excessliquid is removed. The removal of excess liquid may comprise lowering apressure underneath the substrate 22 to a pressure level substantiallybelow the pressure level of the pressure surrounding the substratesupport structure 23. This may be achieved by connecting the areaunderneath the substrate 22 with a low pressure environment, in FIG. 7F,schematically represented by arrows 65.

Due to the resulting difference between a pressure level above theliquid layer 64 and a pressure level below the liquid layer 64, thesubstrate 22 is pulled towards the substrate support structure 23. As aresult, excess liquid is either sucked away via one or more channels 66,for example channels 33 and 35 of the gas distribution system depictedFIG. 3B, and/or squeezed out of the edge of the substrate supportstructure 23, schematically represented in FIG. 7F by arrows 67. Aftersome time, the substrate 22 rests on the contact elements 27 of thesubstrate support structure surface 26.

The removal of excess liquid may further, or alternatively, compriseproviding a gas flow along a circumference of the surface 26. The gasflow is provided at a pressure that is lower than the pressure above thesubstrate 22 so that the substrate 22 remains in contact with thecontact elements. Suitable gases to be used in the gas flow includenitrogen, oxygen and helium.

The gas flow may remove excess liquid in one or more ways. For example,liquid may be swept away by the flow. Additionally, remaining dropletsmay evaporate in the gas flow. Evaporation of remaining droplets may beenhanced by providing dehumidified or “dry” gas, i.e. gas having a vaporcontent of less than 50%, preferably less than 10%, of its vaporsaturation value.

The providing of a gas flow is schematically shown in FIGS. 7G and 7H.Gas is allowed to enter the substrate support structure 23 via channel66 a, while gas is allowed to exit via channel 66 b Channel 66 a andchannel 66 b may correspond to gas inlet 33 and gas inlet 35 in FIG. 3Brespectively. The gas flow is preferably maintained until a capillarylayer 71 is formed, i.e. a thin layer of liquid with a concave outersurface 28 having a pressure below the pressure of its surroundings.Such a capillary layer has been discussed with reference to FIGS. 1 and2.

After formation of the capillary layer due to the removal of excessliquid, the ambient pressure may be lowered. In order to be sure thatthe substrate 22 remains clamped, excess gas, if present, may be removedunderneath the substrate 22, for example via valve 45 as schematicallyshown in FIG. 71.

In embodiments of the invention, after formation of the capillary layer71, vapor may be provided to the capillary layer. The vapor 73 may beprovided by a reservoir 75 at least partly filled with reservoir liquid77. The reservoir 75 may be part of the substrate support structure 23as shown in FIGS. 71 and 7J. Alternatively, the reservoir 75 may be anexternal reservoir. The vapor 73 may then be provided via a transfersystem connectable to both the external reservoir and the substratesupport structure 23.

It must be noted that the liquid vapor reservoir 75 may be provided as aseparate module that can be connected to the substrate support structure23. The provided vapor limits evaporation of liquid from the capillarylayer 71. This may lead to a longer lifetime of the clamp.

FIG. 8 schematically shows a top view of a substrate support structure83 according to a third embodiment of the invention. The substratesupport structure 83 comprises a surface 86 for clamping a substrate.Preferably, the surface is provided with contact elements 87.Additionally, the substrate support structure comprises a gasdistribution system including a moat 91, gas inlets 93, and gas outlets95. Functions of these components have been discussed with reference toFIG. 3A and equally apply for this embodiment. The substrate supportstructure 83 may be used in embodiments of the method of clamping in asimilar way as discussed with respect to substrate support structure 23with reference to FIGS. 7A-7J.

In contrast to embodiments of the substrate support structure 23 shownin FIGS. 3A and 5, substrate support structure 83 comprises a surface 86which is divided in a plurality of sub-surfaces. The sub-surfaces maytake the form of tiles, for example of hexagonal shape, and be arrangedin a tessellated pattern. Each tile may be provided with acircumferential rim (not shown), similar to the circumferential rim 51discussed with reference to FIG. 5. The use of a surface 86 divided in aplurality of sub-surfaces may be beneficial if relatively largesubstrates need to be clamped, for example 300 mm wafers.

FIG. 8B schematically shows a sectional view of a clamp formed by acombination of the substrate support structure 83 of FIG. 8A and asubstrate 82 for illustrative purposes.

FIGS. 9 and 10 schematically show different substrate handling andexposure arrangements which may be used in conjunction with embodimentsof the substrate support structures discussed earlier. FIGS. 9 and 10will be explained with reference to an example related to lithographicprocessing of wafers. It must be understood that the arrangements arenot limited to such an application. FIG. 11 schematically shows anembodiment of a clamp preparation unit that may be used to automateembodiments of a method of clamping a substrate on a substrate supportstructure, for example embodiments explained with reference to FIGS.7A-7J.

Now referring to FIG. 9, in the substrate handling and exposurearrangement, a clamp preparation unit 112 is used to automate a methodof clamping a wafer on a wafer support structure. The clamp preparationunit 112 accepts a wafer to be clamped from a substrate distributionfacility, in this example a so-called wafer track 111. In the clamppreparation unit 112, the clamp is prepared, e.g. by using the methodoutlined with respect to FIGS. 7A-7J. After preparation of the clamp,the clamp is forwarded to a substrate processing unit, in this example alithographic apparatus 113. The lithographic apparatus may comprise aradiation system to provide a patterned beam of radiation, a substratesupport structure to support a substrate, and an optical system toproject the patterned beam of radiation onto a target portion of thesubstrate as will be understood by a person skilled in the art. Furtherdetails regarding operation of an exemplary clamp preparation unit willbe explained with reference to FIGS. 11A-11D.

In FIG. 9, the clamping procedure is schematically denoted by referencenumber 115. Further details regarding operation of an exemplary clamppreparation unit will be explained with reference to FIGS. 11A-11D. Theclamp preparation unit 112 comprises a vacuum system for providing acontrolled pressure environment. The clamping procedure may start withthe introduction of a wafer 122 into the vacuum system of the clamppreparation unit 112, for example by means of a robot arm provided witha wafer support 121 as shown in FIG. 11A.

The wafer 122 may be introduced via a vacuum tight door or a load lockchamber. The wafer support structure 123 may already be present in theclamp preparation unit 112. Alternatively, the wafer support structure123 may be introduced in a similar way as the wafer 122.

Then, liquid may be applied onto the surface of the wafer supportstructure 123 by means of the liquid dispensing unit 124 as shown inFIG. 11A. The liquid dispensing unit 124 provides a liquid flow until aliquid layer of sufficient “thickness” is provided, and then shuts offthe liquid flow. Preferably, the liquid dispensing unit 124 is moveablewithin the clamp preparation unit 112 such that applying of liquid isperformed in an efficient manner without disturbing earlier andsubsequent actions in the clamping procedure. Preferably, the pressurein the clamp preparation unit 112 during applying the liquid onto thesurface of the wafer support structure 123 is below ambient pressure,for example substantially equal to the vapor pressure of the liquid inthe liquid layer. Alternatively, the pressure in the clamp preparationunit may be reduced after applying the liquid but before clamping thewafer.

The wafer 122 and wafer support structure 123 are then moved withrespect to each other to allow placement of the wafer on the liquidlayer 125. For this purpose, the wafer 122 is lowered onto the liquidlayer 125 by means of a substrate transfer unit, for example moveablesupport pins 127 as shown in FIG. 11B. As discussed earlier withreference to FIG. 7D, the first contact between the wafer 122 and theliquid layer 125 may be made at an initial tilt angle alpha (α),preferably less than 10 degrees and preferably greater than 5 degrees.Such tilted placement may be achieved by lowering one side of the wafer122 before lowering the other side of the wafer 122, for example byseparate controlled movement of the support pins 127. Each side of thewafer 122 is lowered until contact is made with the liquid layer 125,and the support pins 127 may then be lowered further and moved out ofthe way. Placement of the wafer 122 on the liquid layer 125 may beperformed at ambient pressure, i.e. about 1 bar. However, placement atlow pressure is preferred, for example a pressure substantially equal tothe vapor pressure of the liquid in the liquid layer.

The wafer support structure 123 may now be connected to one or moreliquid connection units connectable to the wafer support structure 123for removing liquid away from the wafer support structure. In anembodiment, connectors 126 a, 126 b as shown in FIG. 11C may be used forthis purpose. Alternatively, connecting of these one or more liquidconnection units has been established earlier. Excess liquid is removedvia the one or more liquid connection units. Removal of liquid may beperformed at ambient pressure, i.e. about 1 bar.

Furthermore, the wafer support structure 123 may comprise one or moregas connection units for connecting the wafer support structure 123 witha gas supply, for example connectors 126 a, 126 b in FIG. 11C. The gasconnection units may establish an low pressure by “connection” to avacuum. Additionally and/or alternatively, the gas connection units mayprovide a gas flow for enabling formation of a capillary layer betweenthe wafer 122 and the wafer support structure 123 as discussed earlierwith reference to FIGS. 7A-7J. Providing a gas flow may be performed atambient pressure, i.e. about 1 bar. Note that the pressure provided bythe gas flow needs to be lower than the ambient pressure to ensure thatthe wafer 122 keeps its position with respect to the wafer supportstructure 123.

Before forwarding the clamp to the lithographic apparatus 113, asschematically shown in FIG. 11D, the connections 126 a, 126 b areremoved. Forwarding the clamp may be performed by means of a robot aimvia a vacuum tight door or a load lock chamber.

After processing in the lithographic apparatus 113, the clamp may betransferred back to the clamp preparation unit 112 or to a separateunclamping unit for unclamping, i.e. removing the wafer from the wafersupport structure. In FIG. 9, the process of unclamping is schematicallydenoted by reference number 116. Unclamping may be performed byintroducing the clamp into the clamp preparation unit 112, connectingthe one or more liquid connectors to the wafer support structure 123.Via the one or more liquid connectors, additional liquid may be providedto the capillary liquid layer to increase the thickness of the liquidlayer. Additional liquid may be added so that the wafer 122 starts tofloat on top of a liquid layer. The introduction of additional liquidmay be applied in such a way that liquid pressure is substantiallyhomogeneously distributed so that the wafer 122 will not deform orbreak.

At that stage, the wafer 122 may be lifted from the liquid layer on thewafer substrate support surface 123, e.g. by means of support pins 127.The wafer may be lifted at an initial tilt angle, in the reverse of theprocess described above of placing the wafer onto the liquid layer. Theinitial tilt angle during lifting of the wafer is preferably less than10 degrees and preferably greater than 5 degrees, which may be achievedby lifting one side of the wafer before lifting the other side, forexample by separate controlled movement of the support pins. Finally,the wafer 122 may be extracted from the clamp preparation unit 112, forexample by using a robot arm provided with wafer support 121, andtransferred towards the wafer track 111.

In FIG. 9, the clamp preparation unit 112 and the lithographic apparatus113 are depicted as separate units. However, it must be understood thatit is also possible to integrate the clamp preparation unit 112 into alithographic apparatus 113, for example by including the requiredfunctionality of the clamp preparation unit 112 in a load lock of thelithographic apparatus 113. In such a case, wafers will be clamped andunclamped as they enter and exit the lithographic apparatusrespectively.

FIG. 10 schematically shows a different substrate handling and exposurearrangement that may be used in conjunction with embodiments of thesubstrate support structure. In the arrangement of FIG. 10, instead of asingle lithographic apparatus 113 more lithographic apparatus 113 a, 113b, 113 c are used. The functionality of the wafer track 111 and theclamp preparation unit 112 is the same as described with reference toFIG. 9.

In FIG. 10, a clamp ready to be transferred to a lithographic apparatusfor processing may be transferred towards three different lithographicapparatus 113 a, 113 b, 113 c via an additional wafer track 117. Theconfiguration of FIG. 10 may be more efficient if the typical durationof the clamping method to be performed within the clamp preparation unit112 is faster than the typical duration of a lithographic process to beperformed in any one of the lithographic apparatus 113 a, 113 b, 113 c.

Throughout the description, reference has been made to the expression“capillary layer”. The expression “capillary layer” should be understoodto refer to a thin layer of liquid with a concave meniscus shape havinga pressure below the pressure of its surrounding.

Additional aspects of the present invention are further defined in asubstrate support structure for clamping a substrate on a surfacethereof, where the substrate support structure comprises a surface forreceiving a substrate to be clamped by means of a capillary layer of aliquid, a liquid reservoir for storing reservoir liquid and vapor of thereservoir liquid, and a vapor transfer system connecting the reservoirwith the receiving surface such that vapor of the reservoir liquid canbe provided to the capillary layer when present. The reservoir mayextend underneath the receiving surface. Preferably, the reservoircomprises a cavity having a greater portion located underneath thereceiving surface and a lesser portion extending out from acircumference of the receiving surface. The volume for storage of thereservoir liquid in the reservoir may be greater than a volume of thecapillary layer of liquid. The reservoir may be detachable from thereceiving surface. In use, the capillary layer may have a concavelyshaped outer surface, and a free surface area of the liquid in thereservoir is larger than a free surface area of said concavely shapedouter surface. The substrate support structure may further comprise aliquid removal system for removing liquid circumferential to saidsurface. The liquid removal system may comprise a gas distributionsystem. The gas distribution system may comprise at least one gas inletfor providing gas, and at least one gas outlet for removing gas.Alternatively, the gas distribution system may have a plurality of gasinlets and a plurality of gas outlets at equidistant positions withrespect to each other. The substrate support structure may furthercomprise a gas connection unit for connecting the substrate supportstructure with a gas supply. The gas connection unit may be connected tothe vapor transfer system. The vapor transfer system may comprise a flowcontrol unit for separating gas flow via the gas connection unit fromvapor originating from the reservoir. The flow control unit may be avalve or flap. The reservoir of the substrate support structure may belocated in a removable portion of the substrate support structure. Thereservoir and the vapor transfer system may be located in a removableportion of the substrate support structure. The substrate supportstructure may further comprise a sealing structure circumscribing thereceiving surface such that gas provided by the gas distribution systemcan flow between the receiving surface and the sealing structure. Thereceiving surface may be provided with a plurality of contact elements,and wherein the sealing structure has a height corresponding to theheight of the plurality of contact elements. Alternatively, thereceiving surface may further comprise a raised circumferential rim,such that gas provided by the gas distribution system can flow betweenthe circumferential rim and the sealing structure. In such embodiment,the receiving surface may be provided with a plurality of contactelements, and wherein the circumferential rim has a height smaller thanthe height of the plurality of contact elements. The receiving surfacemay be divided into a plurality of sub-surfaces. The liquid removalsystem may then be configured to remove liquid circumferential to eachsub-surface. In case of a plurality of sub-surfaces, at least onesub-surface may have a substantially hexagonal shape.

An additional aspect of the present invention is further defined in amethod for maintaining a substrate clamped to a substrate supportstructure, where the method comprises providing a substrate supportstructure having a surface on which a substrate has been clamped bymeans of a capillary layer, providing a reservoir storing reservoirliquid and vapor of the reservoir liquid, and enabling transfer of thevapor of the reservoir liquid from the reservoir to the capillary layerto limit evaporation from the capillary layer. The substrate supportstructure may be any substrate support structure described earlier.

The invention has been described by reference to certain embodimentsdiscussed above. It will be recognized that these embodiments aresusceptible to various modifications and alternative forms well known tothose of skill in the art without departing from the spirit and scope ofthe invention. Accordingly, although specific embodiments have beendescribed, these are examples only and are not limiting upon the scopeof the invention, which is defined in the accompanying claims.

What is claimed is:
 1. A substrate handling and exposure arrangementcomprising: a plurality of lithography apparatus; a clamp preparationunit for clamping a wafer on a wafer support structure; a wafer track,wherein the clamp preparation unit is configured for accepting a waferfrom the wafer track; and an additional wafer track for transferring theclamp towards the plurality of lithography apparatus.
 2. Arrangementaccording to claim 1, wherein each lithographic apparatus comprises: aradiation system to provide a patterned beam of radiation; and anoptical system to project the patterned beam of radiation onto a targetportion of the wafer.
 3. Arrangement according to claim 1, wherein theclamp preparation unit comprises a vacuum system for providing acontrolled pressure environment.
 4. Arrangement according to claim 3,further comprising a robot arm provided with a wafer support forintroducing the wafer into the vacuum system of the clamp preparationunit.
 5. Arrangement according to claim 3, comprising a vacuum tightdoor or a load lock chamber for introduction of the wafer into the clamppreparation unit.
 6. Arrangement according to claim 1, comprising asecond robot arm and a second vacuum tight door or a load lock chamberfor forwarding the clamp comprising the wafer clamped to the wafersupport structure to the lithographic apparatus.
 7. Arrangementaccording to claim 1, wherein the clamp preparation unit is furtherconfigured for removing the wafer from the wafer support structure. 8.Arrangement according to claim 1, comprising a separate unclamping unitfor removing the wafer from the wafer support structure.
 9. Arrangementaccording to claim 1, wherein the clamp preparation unit comprises oneor more gas connection units for providing and removing gas, and one ormore liquid connection units for providing and removing liquid, andwherein the wafer support structure comprises one or more connectors forconnecting to the one or more gas or liquid connection units. 10.Arrangement according to claim 1, wherein the clamp preparation unitcomprises a liquid dispensing unit for applying liquid onto the surfaceof the wafer support structure, and wherein the wafer support structurecomprises a substrate transfer unit for lowering the wafer onto a liquidlayer formed on the surface of the wafer support structure, and forlifting the wafer from the liquid layer on the wafer support surface,wherein the substrate transfer unit comprises a plurality of separatelycontrolled movable support pins.
 11. Method of handling and processingsubstrates, comprising: providing a clamp preparation unit, the clamppreparation unit accepting a wafer to be clamped from a wafer track;preparing the clamp in the clamp preparation unit; forwarding theclamped wafer to one of a plurality of lithographic apparatus;processing the wafer in the lithographic apparatus; transferring theclamp back to the clamp preparation unit or to a separate unclampingunit; unclamping the wafer; extracting the wafer from the clamppreparation unit; and transfer the wafer towards the wafer track. 12.Method according to claim 11, wherein the wafer is introduced into avacuum system of the clamp preparation unit by means of a robot armprovided with a wafer support.
 13. Method according to claim 11, whereinthe wafer is introduced into a vacuum system of the clamp preparationunit via a vacuum tight door or a load lock chamber.
 14. Methodaccording to claim 11, wherein the wafer support structure is alreadypresent in the clamp preparation unit.
 15. Method according to claim 11,wherein the wafer support structure is introduced into the clamppreparation unit in a similar way as the wafer.
 16. Method according toclaim 11, further comprising: applying liquid onto the surface of thewafer support structure by means of a liquid dispensing unit; moving thewafer and the wafer support structure with respect to each other; andsubsequently lowering the wafer onto the liquid layer by means of asubstrate transfer unit, said substrate transfer unit comprising aplurality of separately controlled movable support pins.
 17. Methodaccording to claim 11, further comprising extracting the wafer from theclamp preparation unit by using a robot arm provided with wafer support,and transferring the wafer back toward the wafer track.
 18. Methodaccording to claim 11, wherein the duration of the clamping methodperformed in the clamp preparation unit is shorter than the duration ofa lithographic process to be performed in one of the lithographicapparatus.